The Torino scale was introduced by Richard Binzel, who has now been working on the project for 10 years, and was adopted by the International Astronomical Union in June 1999.
It is used to quantify the risks of Earth-grazing bodies such as asteroids and comets so as to improve communication of the potential risks that these objects present for the Earth.
It takes into account several factors: the size and velocity of the celestial object and its trajectory. Values are given from 0 to 10, without any decimal values. This "score" is given before each passage of the celestial object close to the Earth.
The scale uses a colour code
|Events of no consequence ||0||The likelihood of a collision is zero, or is much lower than the probability of a random object of the same size hitting the earth in the next few decades. This category also includes any object, which in the context of a possible collision, has no chance of reaching the planet's surface.|
|Events that merit consideration ||1|
The chances of collision are highly improbable. New telescopic observations will very likely will lead to the object being declassified from level 1 to level 0.
|Events meriting attention by astronomers ||2|
A collision is highly unlikely but the trajectory is close to the Earth. While meriting attention by astronomers, there is no cause for public attention or public concern. New telescopic observations will very likely lead to declassification to Level 0. As our means of observation develop, many asteroids should be discovered in the next few years that will be classified at level 2.
|3||A close encounter, a 1% maximum chance of collision with localized damage. New telescopic observations will very likely lead to declassification to Level 0. Attention by public and the authorities is required if the risk of collision is less than a decade away.|
|4||A close trajectory with a 1% chance of collision capable of regional devastation. New telescopic observations will very likely lead to declassification to Level 0. Attention by public and by public authorities is required if the risk of collision is less than a decade away.|
|Threatening events ||5|
A close trajectory posing a serious threat of a collision causing regional devastation. If the encounter is less than a decade away, governmental contingency planning must be considered.
|6||A close trajectory posing a serious threat of a global catastrophe. If the encounter is less than a decade away, governmental contingency planning must be considered. Precise observations of the object are required.|
|7||A close trajectory which poses an unprecedented threat of a global catastrophe. For such a threat in less than 100 years, international contingency planning must be undertaken, especially to determine urgently and conclusively whether a collision will occur.|
A certain collision capable of causing localized destruction. Such events occur on average between once every 50 years to 1000 years. (The last one occurred in Siberia at the beginning of the last century).
|9||A collision is certain, causing regional devastation. Such events occur on average between once every 10,000 to 100,000 years.|
|10 ||A collision is certain causing a global climatic catastrophe that may threaten the future of the human species. Such events occur on average once every 100,000 years, or less often.|